The so-called resist-heating effect that occurs during variable-shaped-spot beam delineation (using, e.g., an electron beam) is well known. As a result of resist heating, the size of a pattern feature as transferred is smaller when a beam with a small transverse surface area is used for delineation, compared to when a beam with a larger transverse surface area is used. The resist-heating effect arises due to increases in resist temperature as the resist is being exposed by an electron beam, with consequent increase in resist sensitivity. The resist-heating effect is not limited to variable-shaped-spot beam delineation, but rather is encountered in all technologies utilizing a charged particle beam to transfer a pattern having features with various shapes and surface areas.
The resist-heating effect can be corrected in conventional variable-shaped-spot beam delineation methods by changing the exposure dose (e.g., by changing the exposure duration) applied by the shaped beam directed to an exposure unit of the pattern. See Japanese published patent document no. Kokai Hei 2-143516. However, the resist-heating effect conventionally cannot be corrected in charged-particle-beam projection-exposure systems by changing the duration of exposure applied to any of the exposure units of the pattern.
In one type of conventional hybrid exposure (Japanese patent publication no. Kokai Hei 8-314121) termed a "cell projection" method, regions on a reticle having a high density of pattern openings (e.g., for memory chips) are divided into cells each having a smaller number of openings than required for a conventional feature pattern. In such methods, however, uneven edges of features can occur.
A reticle used for electron-beam projection microlithography can be a "stencil" reticle or a "scattering" ("membrane") reticle. (U.S. Pat. No. 5,130,213.) Using a stencil reticle, it not possible to define a donut-shaped feature. As a result, a stencil reticle having such a feature is divided into two complementary stencil reticles each defining a portion of such a feature. The resulting double exposure of certain features can cause resist-heating effects. Unfortunately, no technology exists for correcting the resist-heating effect encountered with use of complementary stencil reticles. Scattering reticles are also subject to resist-heating effects, especially with relatively large features defined by such reticles.